Multivalent metal ion extraction using diglycolamide-coated particles

ABSTRACT

A separation medium, a method for using that separation medium and an apparatus for selectively extracting multivalent cations such as pseudo-lanthanide, prelanthanide, lanthanide, preactinide or actinide cations from an aqueous acidic sample solution is described. The separation medium is preferably free-flowing and comprises particles having a diglycolamide (DGA) extractant dispersed onto an inert, porous support.

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This is a continuation-in-part of application Ser. No. 10/261,031filed Sep. 30, 2002.

TECHNICAL FIELD

[0002] The present invention is concerned generally with a method,separation medium and apparatus for selectively extracting multivalentcations from acidic aqueous solutions. More particularly, the inventionis concerned with a separation medium that is preferably free-flowingand is comprised of a diglycolamide dispersed onto an inert substratematerial, a method for using that separation medium and an apparatus forselectively extracting multivalent cations from an acidic aqueoussample.

BACKGROUND OF THE INVENTION

[0003] The wide-scale use of nuclear technology in power production andin nuclear weapons manufacturing has necessitated the periodicmonitoring of biological and environmental samples for the presence ofselected elements such as strontium (Sr), cerium (Ce), europium (Eu),actinium (Ac), thorium (Th), uranium (U,) neptunium (Np), plutonium(Pu), americium (Am), and curium (Cm), and for monitoring particularnuclides such as ⁹⁰Sr, ¹⁴⁴Ce, and ^(152,154)Eu. There is, therefore, aclear need for an analytical procedure and methodology suitable for usein the routine monitoring of persons whose activities expose them to therisk of internal contamination from these elements and for thedetermination of the levels of radionuclides in various environmentalsamples (e.g., soils, plants, natural waters, and waste streams). Anumber of procedures for the selective recovery of the above elementshave been disclosed.

[0004] U.S. Pat. No. 4,548,790 dated Oct. 22, 1985 describes a group ofneutral bifunctional organophosphorus compounds broadly described asalkyl (phenyl)-N,N-dialkylcarbamoylmethylphosphine oxides (hereinafterreferred to as CMPO) that are useful for the recovery of actinide andlanthanide cations from acidic solutions. The combination of the CMPOwith a phase modifier such as tri-n-butyl phosphate (hereinafterreferred to as TBP) in a normal paraffin hydrocarbon diluent isdescribed in U.S. Pat. No. 4,574,072 dated Mar. 4, 1986.

[0005] U.S. Pat. No. 4,835,107 dated Oct. 21, 1986 describes a methodfor the concentration and separation of actinide cations from biologicaland environmental samples using CMPO and TBP in a chromatographic mode.The CMPO/TBP chromatographic system was applied in the recovery andpurification of yttrium-90 for medical applications described in U.S.Pat. No. 5,368,736 dated Nov. 29, 1994. Other systems utilizingmonofunctional, as well as bifunctional, organophosphorus extractants inthe recovery of lanthanide and actinide cations from acidic media inboth the liquid-liquid extraction mode and in the extractionchromatographic mode are described in Kimura (1990) J. Radioanal. Nucl.Chem., 141, 295 and Ramanujam et al. (1995) Solvent Extr. Ion Exch.,13(2), 301-312.

[0006] U.S. Pat. Nos. 5,100,585, 5,110,474 and 5,346,618 by some of thepresent inventors teach the manufacture and use of a chromatographicmedium for selectively separating strontium or technetium cations fromacidic compositions from various sources. The solid phasechromatographic medium made and used in those patents comprised asolution of a Crown ether dissolved in a diluent that was slightlysoluble or insoluble in water, but capable of dissolving a substantialquantity of water, such as octanol, which solution was itself dispersedonto a solid inert resin substrate material.

[0007] A few years after the filing of the applications that became theabove U.S. patents, Benzi et al. (1992) J. Radioanal. Nucl. Chem.,Letters, 164(4):211-220 reported on the use of 18-Crown-6 (18C6),dibenzo-18-Crown-6 (DB18C6) and 24Crown-8 (24C8) as well as open chainligands (podands) adsorbed on Amberlite® XAD-4 and XAD-7 resins orKieselgel as supports for removal of radium cations from aqueoussolutions. Those authors reported the supported crown ethers to beinefficient for that extraction, whereas the supported open chainligands were said to provide satisfactory distribution coefficients forthe removal of radium.

[0008] The above-noted patents of some of the present inventors provideda large technological advance over the liquid-liquid separationtechniques that preceded them, and from which their technical advancegrew. However, the separation medium of those patents exhibited changesupon elution of the captured strontium cations that minimized theirusefulness for a subsequent separation, including loss of diluent to theeffluent medium. Still further, the amount of strontiumcation-extracting Crown ether present on any given support was limitedbecause of the presence of the diluent.

[0009] All of the prior methods suffer from one or more majordisadvantages. Foremost among these is that the retention of thetrivalent lanthanides and actinides in acidic aqueous nitric andhydrochloric acid is limiting and the subsequent recovery in dilute acidis difficult, especially in the case of tetra- and hexavalent actinides.In the chromatographic mode, low retention of the analyte in the columnloading step results in its early breakthrough in the column effluent.Early breakthrough frequently results in losses of analyte andinsufficient purification because of limited column rinsingcapabilities.

[0010] In recent years, the wide-scale use of nuclear technology hasalso expanded greatly in the field of medicine. The use of radioactivematerials in diagnostic medicine is now readily accepted because theseprocedures are safe, minimally invasive, cost-effective, and theyprovide unique information that is otherwise unavailable to theclinician. More recently, radioactive isotopes are being used to treatdisease as opposed to diagnosing disease. This technique is referred toas radioimmunotherapy (RIT). The U.S. Food and Drug Administration (FDA)has approved the use of the first RIT drug that relies on radioactivedecay to impart the cytotoxic effect to the disease site.

[0011] The FDA has mandated rigorous purity requirements forradionuclides used for therapeutic applications. Foremost among theserequirements is high radionuclidic purity, which stems directly from thehazards associated with the introduction of long-lived or high-energyradioactive impurities into a patient. Chemical purity is also vital toa safe and efficient medical procedure because the radionuclide mustgenerally be bonded to a biolocalizing agent prior to use. Biolocalizingagents have extremely low capacities for metal ions and, therefore, thepresence of ionic interferents can inhibit the uptake of the medicallyuseful radionuclide. Another critical factor in bonding the radionuclideto the biolocalizing agent is obtaining the desired purifiedradionuclide in a dilute ≦0.1 M acidic (usually HCl) aqueous solution. Anumber of pseudo-lanthanide, prelanthanide, lanthanide, preactinide andactinide nuclides are candidates for use in radioimmunotherapy; forexample, ⁴⁷SC, ⁹⁰Y, ¹⁴⁹Pm, ¹⁵³Sm, ¹⁵³Gd, ¹⁶⁶Ho, ¹⁷⁷Lu, ²²⁵Ac, and ²⁵⁵Fm.

[0012] In related studies, Sasaki et al. [Sasaki et al. (2001) SolventExtr. Ion Exch., 19(1):91-103; and Sasaki et al. (2002) Solvent Extr.Ion Exch., 20(1):21-34. See also the web site of the Japanese AtomicEnergy Research Institute (JAERI) and Japanese Kokai No. 2002-1007 andNo. 2002-243890.] have published results on the liquid-liquid extractionof trivalent lanthanides and tri-, tetra-, and hexavalent actinides withstructurally tailored diamides including selected diglycolamides.However, these studies were carried out using very dilute solutions ofthe extractants in nitrobenzene, chloroform, toluene, hexane, orn-dodecane. The aqueous phase was primarily nitric acid or 0.1 M sodiumperchlorate and, in the case of trivalent lanthanides and actinides,never exceeded 1 M in concentration. Extrapolation of these data to auseful extraction chromatographic system that can achieve the objectivescited herein cannot be done.

[0013] It has been demonstrated in related studies by Cortina et al.(1994) Solvent Extr. Ion Exch., 12(2):371-391, that quantitativepredictions of metal ion uptake from liquid-liquid extraction datacannot be extended to extraction chromatographic systems. These studieshave shown that the selectivity order for the extraction of Cu and Cd(Cu greater than Cd) by bis-2-ethylhexyl phosphoric acid (HDEHP) isreversed for the solid supported reagent. Studies by Miralles et al.(1992) Solvent Extr. Ion Exch. 10(1):51-68 and Casas et al. (1989)Polyhedron 8:2535 have shown that the nature of the metal speciesextracted by HDEHP in toluene or paraffinic hydrocarbons is somewhatdifferent from the same extractant sorbed on Amberlite® XAD-2. Theextracted species is typically less solvated in the extractionchromatographic system than in the liquid-liquid extraction system. Noneof the above observations are surprising because the film thickness ofan extractant sorbed on a porous solid support having a surface area of400 to 500 m²/g, for example Amberchrom® CG-71, and containing 40 weightpercent of an extractant with a density of 0.95 g/mL is only about 1 to2×10⁻³ μm. It is not, therefore, unexpected that the physical andchemical properties of the extractant and the concomitant extractionbehavior in extraction chromatographic resins are different than in aliquid-liquid extractant system.

[0014] It would therefore be beneficial to provide a method, separationmedium and apparatus for separating multivalent cations from acidicaqueous samples such as biological, commercial waste and environmentalsamples that do not exhibit the negative attributes of the priortechnologies. The method, separation medium and apparatus of the presentinvention that are described hereinafter can overcome those negativeattributes, while maintaining the previously achieved advances.

BRIEF SUMMARY OF THE INVENTION

[0015] The present invention contemplates a separation medium, anapparatus for carrying out a separation such as a chromatographic columnor cartridge containing the separation medium, and a method of using theseparation medium to separate a preselected multivalent metal cationsuch as a pseudo-lanthanide [e.g., scandium(III) and yttrium(III)], aprelanthanide [lanthanum(III)], a lanthanide, a preactinide[actinium(III)] or an actinide cation, like trivalent americium (Am³⁺),yttrium (Y³⁺) and ytterbium (Yb³⁺) cations from other cations such asradium (Ra²⁺) cations present in an acidic aqueous solution. Acontemplated preselected multivalent metal cation, other than cadmium,typically has a crystal ionic radius in {dot over (A)}ngstrom units ofabout 0.8 to about 1.2. The separation medium comprises particles havinga diglycolamide (DGA) extractant dispersed onto an inert, porous supportsuch as polymeric resin or silica particles. The separation medium ispreferably free of an organic diluent, although such a diluent can bepresent. A contemplated diglycolamide extractant corresponds instructure to Formula I

[0016] wherein R¹, R², R³ and R⁴ are the same or different and arehydrido (hydrogen) or hydrocarbyl groups such that R¹+R²+R³+R⁴ containsabout 14 to about 56 carbon atoms, and preferably about 16 to about 40carbon atoms. More preferably each of R¹, R², R³ and R⁴ is a hydrocarbylgroup. Most preferably, each of R¹, R², R³ and R⁴ is the samehydrocarbyl group.

[0017] A method for separating a predetermined multivalent cation havinga crystal ionic radius of about 0.8 to about 1.2 {dot over (A)}ngstroms(Å) from an aqueous sample that contains additional mono- or multivalentmetal cations, or both, is also contemplated. The aqueous sample alsocontains a salting out amount of one or more salting out agents for aneutral extractant such as high concentrations of nitric, hydrochloric,perchloric, or the like acids, or lithium nitrate, aluminum nitrate,lithium chloride or the like.

[0018] That method includes the steps of contacting an above-describeddiglycolamide-containing separation medium with an aqueous samplecontaining dissolved multivalent cations, including the predeterminedmultivalent cation. That contact is maintained for a time periodsufficient for the multivalent cations to be extracted from the samplesolution to the separation medium to form a solid phase-loadedseparation medium and a liquid phase multivalent cation-depleted sample.The solid and liquid phases are thereafter separated. The multivalentcation is thereafter preferably eluted by contacting the loadedseparation medium with water or dilute hydrochloric or nitric acids.

[0019] A separation apparatus for extracting multivalent cations from anacidic aqueous solution comprising the above separation medium in asupport vessel is also contemplated. A contemplated apparatus has afluid inlet and fluid outlet and one or more porous supports within thevessel for maintaining the separation medium in a desired position. Acontemplated support vessel is typically glass or plastic such aspolyethylene or polypropylene and is typically a chromatographic columnor cartridge.

[0020] The present invention has several benefits and advantages.

[0021] One benefit of the invention is provision of a novel extractionchromatographic material for the separation of multivalent cations suchas those of Sc, Y, and lanthanides and actinides from biological,environmental and strongly acidic solution samples that contain othermetal cations and for use in nuclear medicine.

[0022] An advantage of the invention is the provision of an improvedmaterial for sorption of the above multivalent cations on a support from(a) strongly acidic nitric acid solution and the provision forrecovering (stripping) those cations in dilute nitric acid solution, aswell as sorption from (b) strongly acidic hydrochloric acid solution andthe provision for recovering (stripping) of those cations in a dilutehydrochloric acid solution, and sorption from (c) from strongly acidicnitric acid solution and recovering those cations in a dilutehydrochloric acid solution.

[0023] Another benefit of the invention is the provision of an improvedmaterial for the sorption of those multivalent cations on an extractionmedium from an aqueous solution of nitrate or chloride salting out agentsalts such as lithium nitrate or chloride and aluminum nitrate andrecovering those cations in dilute hydrochloric and nitrate acidsolutions.

[0024] Another advantage of the present invention is the unexpecteddifference in D_(w) values observed for separation media between 0.1 and3 M nitric or hydrochloric acids for particular trivalent metal cationswhen using a diglycolamide extractant having four 2-ethylhexyl amidonitrogen substituents as compared to a diglycolamide extractant havingfour n-octyl substituents.

[0025] Still further benefits and advantages will be apparent to theskilled worker from the disclosure that follows.

BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In the drawings forming a portion of this disclosure, and inwhich like last two digit numbers indicate like structures,

[0027]FIG. 1 shows a schematic representation of a separation vesseluseful in an embodiment of the invention;

[0028]FIG. 2 shows schematic representation of another separation vesseluseful in an embodiment of the invention;

[0029]FIG. 3 is a plot of D_(w) vs. [HNO₃] for uptake of Ba(II)(circles), Ce(III) (triangles), and Th(IV) (squares) byN,N,N′,N′-tetra-n-octyl-DGA resin, using a contact time of 1 hour at 25°C.;

[0030]FIG. 4 is a plot of D_(w) vs. [HCl] for uptake of Ba(II)(circles), Ce(III) (triangles), and Th(IV) (squares) byN,N,N′,N′-tetra-n-octyl-DGA resin, using a contact time of 1 hour at 25°C.;

[0031]FIG. 5 is a plot of D_(w) vs. [HNO₃] for uptake of Ce(III)(circles) , Eu(III) (squares), and Y(III) (triangles) byN,N,N′,N′-tetra-n-octyl-DGA resin, using a contact time of 1 hour at 25°C.;

[0032]FIG. 6 is a plot of D_(w) vs. [HCl] for uptake of Ce(III)(circles) , Eu(III) (squares), and Y(III) (triangles) byN,N,N′,N′-tetra-n-octyl-DGA resin, using a contact time of 1 hour at 25°C.;

[0033]FIG. 7 is a plot of D_(w) vs. [HNO₃] for uptake of Ce(III)(circles) , Eu(III) (squares), and Y(III) (triangles) byN,N′-dihexyl-N,N′-dimethyl-DGA resin, using a contact time of 1 hour at25° C.;

[0034]FIG. 8 is a plot of D_(w) vs. [HCl] for uptake of Ce(III)(circles) , Eu(III) (squares), and Y(III) (triangles) byN,N′-dihexyl-N,N′-dimethyl-DGA resin, using a contact time of 1 hour at25° C.;

[0035]FIG. 9 is a plot of D_(w) vs. [HNO₃] for uptake of Ce(III)(circles) , Eu(III) (squares), and Y(III) (triangles) byN,N,N′,N′-tetra- (2-ethylhexyl)-DGA resin, using a contact time of 1hour at 25° C.;

[0036]FIG. 10 is a plot of D_(w) vs. [HCl] for uptake of Ce(III)(circles) , Eu(III) (squares), and Y(III) (triangles) byN,N,N′,N′-tetra- (2-ethylhexyl)-DGA resin, using a contact time of 1hour at 25° C.; and

[0037]FIG. 11 is a chromatogram showing cpm/mL vs. Bed Volumes of Eluatefor the elution of Ra(II) (circles) and Ac(III) (triangles) on a 0.50 mLbed of N,N,N′,N′-tetra-n-octyl-DGA resin at 25° C.

DETAILED DESCRIPTION OF THE INVENTION

[0038] The present invention contemplates separation of a polyvalentmetal cation from an aqueous sample composition. A contemplatedmultivalent metal cation typically exhibits a valence of +3, +4 or +6,although some +2 cations can also be selectively separated. A moreconvenient way to generically characterize a contemplated cation is byits valence in aqueous solution being +2 or greater and exhibiting acrystal ionic radius of about 0.8 to about 1.2 {dot over (A)}ngstroms(Å), and more preferably about 0.9 to about 1.2 Å. All of themultivalent cations examined thus far, with the exception of cadmium,that exhibit the above crystal ionic radius selectively bind to acontemplated separation medium.

[0039] Aside from cadmium, the size to capacity for separation on acontemplated separation medium works for the almost twenty multivalentcations studied thus far. Crystal ionic radii can be obtained from atable in the Handbook of Chemistry and Physics, 54^(th) ed., CRC Press,Cleveland Ohio, pages F-194-F195 (1964).

[0040] A contemplated multivalent cation is present in an aqueous samplethat contains one or both of a monovalent cation and a multivalentcation. The aqueous sample also contains a salting out amount of one ormore salting out agents for a neutral extractant such as highconcentrations of nitric, hydrochloric, perchloric acids or the like orlithium nitrate, aluminum nitrate, lithium chloride or the like, as areknown in the art. Thus, the salting out agent facilitates aniontransport with the separated multivalent cations from the aqueous phaseto the contemplated separation medium. Exemplary salting out amounts areillustrated hereinafter and include concentrations of acid of about 0.1M to concentrated, but are more usually about 4 to about 8 M, withnitric acid being a preferred salting out agent. Lithium nitrate andlithium chloride are typically used at about 0.5 M to their respectivesolubility limits, whereas aluminum nitrate is typically used at about0.2 M to its solubility limit.

[0041] A contemplated separation medium that can be used to bindmultivalent cations such as the pseudo-lanthanide, prelanthanide,lanthanide, preactinide or actinide cations in the presence of one orboth of multivalent and monovalent cations is comprised of adiglycolamide (DGA) extractant dispersed on inert solid phase supportparticles. A contemplated diglycolamide extractant corresponds instructure to Formula I

[0042] wherein R¹, R², R³ and R⁴ are the same or different and arehydrido (hydrogen) or hydrocarbyl groups such that R¹+R²+R³+R⁴ containsabout 14 to about 56 carbon atoms. Preferably, R¹+R²+R³+R⁴ containsabout 16 to about 40 carbon atoms. More preferably each of R¹, R², R³and R⁴ is a hydrocarbyl group. Most preferably, each of R¹, R², R³ andR⁴ is the same alkyl, hydrocarbyl group.

[0043] The word “hydrocarbyl” is defined to include straight andbranched chain aliphatic as well as alicyclic groups or radicals thatcontain only carbon and hydrogen. Thus, alkyl, alkenyl and alkynylgroups are contemplated, as are aromatic hydrocarbons such as phenyl andnaphthyl groups, and aralkyl groups such as benzyl and phenethyl groups.Where a specific hydrocarbyl substituent group is intended, that groupis recited; that is, C₁-C₄ alkyl, methyl or dodecenyl. Exemplaryhydrocarbyl groups contain a chain of 1 to about 18 carbon atoms, andpreferably two to about 10 carbon atoms.

[0044] A particularly preferred hydrocarbyl group is an alkyl group.Illustrative alkyl groups include methyl, ethyl, propyl, iso-propyl,butyl, hexyl, octyl, nonyl and decyl groups. Particularly preferredalkyl groups are the n-octyl and the 2-ethylhexyl groups.

[0045] A contemplated separation medium comprises a diglycolamideextractant coated on inert, solid phase support particles. Contemplatedsolid phase support particles are inert in that they do not react withthe aqueous acid, such as the aqueous nitric acid that is present in acontemplated separation, or with the extractant.

[0046] A contemplated inert, porous support is itself preferablyfree-flowing when dry, and can be made of a variety of materials,including silica and polymeric resin as known in the art for use in achromatographic column. By “free-flowing”, it is meant that the supportand separation medium are pourable particles that are free fromsubstantial clumping. Thus, for example, a beaker of dry contemplatedsupport particles or dry separation medium particles pours much like drysilica gel powder used for column chromatography.

[0047] Exemplary silica-based support particles are available from SigmaChemical Co. (St. Louis, Mo.) under the designation controlled-poreglass and controlled-pore glyceryl-glass. These materials are availablein varying mesh sizes from 20-80 to 200-400 and in varying nominal poresizes from 75 through 3000 Å. Useful trimethylsilyl-bonded porous silicaparticles are available from Alltech Associates, Deerfield, Ill. Theseparticles have a nominal pore size of 300 Å and are available in 90-130,20-50 and 35-70 micron diameters.

[0048] Exemplary useful polymeric resins include the Amberlite®polyaromatic resins such as those sold under the designations XAD-4,XAD-8, XAD-11 and XAD-16, and the acrylic resin sold under thedesignation XAD-7 by Rohm and Haas Co., Philadelphia, Pa. and areavailable in 20-60 mesh size. These resin particles are said to have thefollowing average pore diameters and surface areas: XAD-4 40 Å and 725m²/g; XAD-7 90 Å and 450 m²/g; XAD-16 100 Å and 800 m²/g, and arereferred to in the art as macroreticular resins. Illustrative sphericalrigid bead macroreticular Amberchrom® resins such as those sold underthe designations CG-161, CG-300, CG-100 for styrene/divinylbenzene-containing materials, and CG-71 for amethacrylate/dimethacrylate-containing material are also useful. Theselatter resin particles are commercially available from TosoHaas,Montgomeryville, Pa. Each of the latter four resins is available inthree particle size ranges: “s” or superfine at 20-50 μm, “m” or mediumat 50-100 μm, and “c” or coarse at 80-160 μm. Typical resin particlesare reported to have the following average pore sizes and surface areas:CG-161 150 Å and 900 m²/g; CG-300 300 Å and 700 m²/g; CG-1000 1000 Å and200 m²/g; and CG-71 250 Å and 500 m2/g. It is understood that theAmberlite® XAD-7 and Amberchrom® CG-71 are chemically similar materials,as are Amberlite® XAD-4 and Amberchrom® CG-161.

[0049] A contemplated polymeric resin support is typically sufficientlyhydrophilic and wettable that when placed in distilled water and shaken,the resin sinks rather than floats. A more quantitative determination ofa satisfactory support can be found in the water regain values discussedin Parrish (1977) Anal. Chem., 49(8):1189-1192 and Parrish (1965) J.Appl. Chem. (London), 15:280-288. Using water regain values, acontemplated resin exhibits a water regain value greater than about0.75, and less than about 3.5. A preferred resin exhibits a water regainvalue of about 1 to about 2.5, and more preferably about 1.75 to about2.25.

[0050] A contemplated support has sufficient porosity that it can adsorbdiglycolamide extractant loaded (coated) in an amount of about 3 toabout 50 weight percent of the total separation medium weight and stillremain free-flowing when dry. The diglycolamide extractant is morepreferably present at about 10 to about 40 weight percent of theseparation medium, and more preferably still at about 20 to about 40weight percent in the absence of diluent. When diluent is present, thediglycolamide portion can be about 3 to about 30 weight percent of theseparation medium.

[0051] A contemplated support is also preferably particulate. By “dry”,it is meant that the separation medium loses less than about 5 weightpercent after being held at a temperature of 50° C. at a pressure of 0.1mm of mercury for 24 hours.

[0052] More specifically, a preferred solid phase separation medium iscomprised of free-flowing particles that contain about 40 weight percentN,N,N′,N′-tetra-n-octyl diglycolamide (TO-DGA) extractant coated onAmberchrom -CG71, and is referred to as Yttrium Resin. The Yttrium Resinis now commercially available from Eichrom Technologies, Inc.

[0053] The diglycolamide extractant can be present in a contemplatedextraction medium alone or it can be dissolved in an organic diluent.When a diluent is present, the extraction medium particles may adhere toeach other (cohere), rather than being free flowing as are particles ofdry sand, which is preferred. A contemplated separation medium ispreferably free of an organic diluent, and preferably free of a diluentthat is (i) insoluble or has limited (sparing) solubility in water and(ii) capable of dissolving a substantial quantity of water.

[0054] The amount of diglycolamide extractant in the diluent can varydepending upon the particular diglycolamide utilized. For example aconcentration of about 0.1 to about 0.5 M of the tetraoctyl form in thediluent is satisfactory, with about 0.2 M being preferred.Concentrations above about 0.5 M of the diglycolamide in the diluenttend not improve multivalent metal ion recovery. Other diglycolamidederivatives can be present at about 0.1 to about 1.5 molar in thediluent.

[0055] The diluent is an organic compound that has a relatively highboiling point; that is, about 170 degrees to about 220 degrees C atatmospheric pressure, limited or no solubility in water; that is, about0.5 weight percent or less, and in which the diglycolamide is soluble.Some of the diluents contemplated can dissolve about 0.5 to about 6.0 Mof water.

[0056] Particularly preferred diluents are hydrocarbons such as decane,dodecane, decalin, diethylbenzene and diisopropylbenzene. Otherillustrative diluents include alcohols, ketones, carboxylic acids,esters and nitroaromatics such as nitrobenzene. Suitable alcoholsinclude 1-octanol, 1-heptanol and 1-decanol. The carboxylic acidsinclude octanoic acid, heptanoic and hexanoic acids. Ketones that meetthe criteria can be either 2-hexanone or 4-methyl-2-pentanone, whereasthe esters include butyl acetate and amyl acetate.

[0057] The extractant such as N,N,N′,N′-tetra-n-octyl diglycolamide(TO-DGA) and similar tetraalkyl diamides dissolved in a water-insolubleorganic solvent such as nitrobenzene, chloroform, toluene or an alkanesuch as n-hexane or n-dodecane reported to be useful for theliquid/liquid extraction of lanthanide and actinide cations from aqueousnitric and perchloric acid solutions are known. [Sasaki et al. (2001)Solvent Extr. Ion Exch., 19(1):91-103; and Sasaki et al. (2002) SolventExtr. Ion Exch., 20(1):21-34. See, also the web site of the JapaneseAtomic Energy Research Institute (JAERI) and Japanese Kokai No.2002-1007 and No. 2002-243890.] In those studies, the synthesis ofN,N,N′,N′-tetra(2-ehtylhexyl) diglycolamide not reported nor was thecation partitioning behavior of this extractant ever reported by theseauthors. That is a new compound.

[0058] The extractant such as N,N,N′,N′-tetra-n-octyl diglycolamide(TO-DGA) can be mixed with a lower boiling organic solvent such asmethanol, ethanol, acetone, diethyl ether, methyl ethyl ketone, hexanes,or toluene and coated onto an inert support, such as glass (silica)beads, polypropylene beads, polyester beads, or silica gel.

[0059] A method for separating a preselected multivalent lanthanide oractinide cation from an aqueous sample containing additional polyvalentmetal cations is contemplated. That method includes the steps ofcontacting an above-described separation medium with an acidic aqueoussample containing dissolved multivalent cations, including thepredetermined lanthanide or actinide cation. That contact is maintainedfor a time period sufficient for the multivalent lanthanide or actinidecations to be extracted from the sample solution to the separationmedium to form a solid phase loaded separation medium and a liquid phasemultivalent lanthanide or actinide cation-depleted sample. The solid andliquid phases are thereafter separated. The lanthanide or actinidecation is thereafter preferably eluted from the loaded separation mediumby contacting the loaded separation medium with water or dilutehydrochloric acid. The contact is typically carried out at an aciditynear the maximum for the cation(s) to be separated (extracted), such asat an acid concentration near that at which the separation mediumreaches maximal extraction.

[0060] Extraction of the lanthanide or actinide cations from thesolution to the separation medium to form a solid phase loadedseparation medium is typically a rapid event. Thus, gravity feed of alanthanide or actinide cation-containing aqueous sample solution througha typically dimensioned chromatographic column containing the separationmedium with little retardation of the flow rate typically provides asufficient contact maintenance time. Swirling of the sample solution andseparation medium for a few minutes in a flask or beaker is alsotypically sufficient contacting.

[0061] Separation of the solid and liquid phases is also readilyachieved. Where a column or cartridge is used as the separationapparatus, passage of the liquid phase lanthanide or actinidecation-depleted sample out of the vessel is sufficient to effect thedesired solid/liquid phase separation. Where a beaker, flask or othervessel is used for the separation, simple decantation can be used toeffect the separation of phases. One can also use aqueous lithiumnitrate, lithium chloride or aluminum nitrate in a wash or rinsing stepto assist in eluting interfering cations that may be maintained in theload solution present in the interstices between particles.

[0062] In preferred practice, the desired lanthanide or actinide cationsare selectively eluted from the loaded separation medium by contactingthe loaded separation medium with an aqueous solution having a pH valueof about 1 or less, or with plain distilled or deionized or even tapwater. The elution solution need not be distilled or deionized water,although such water is preferred. Typically, aqueous 0.1 M HCl isutilized to elute lanthanide or actinide cations from the separationmedium. The concentration of nitrate anions is also preferably less thanor equal to about 0.1 molar.

[0063] The contacting of the separation medium with the aqueous acidiclanthanide or actinide cation-containing sample can be carried out in anopen or closed vessel in which the solid and liquid are swirled orstirred together. It is more preferred, however, that that contactingstep be carried out in a below-described support vessel such as achromatographic separation column or cartridge by passing the aqueousacidic sample solution through the vessel, and that the preferredelution of lanthanide or actinide cations be carried out by passingwater or dilute hydrochloric acid (at a concentration of about 0.1 M orless) through the loaded separation medium in the support vessel.

[0064] An apparatus for separating lanthanide or actinide cations suchas yttrium or actinium cations from an acidic aqueous solutioncomprising the above separation medium in a support vessel is alsocontemplated. A contemplated support vessel is typically glass orplastic such as polyethylene or polypropylene and is typically achromatographic column or cartridge. A contemplated vessel can includeone or more inlets, outlets, valves such as stopcocks and similarappendages.

[0065] One contemplated support vessel is cylindrical and has an inletfor receiving an aqueous sample solution prior to contact of the samplesolution with the contained separation medium and an outlet for theegress of water or other liquid after contact with the medium. When thesupport vessel is a glass or plastic chromatographic column orcartridge, the vessel can contain appropriate valves such as stopcocksfor controlling aqueous flow, as are well-known, as well as connectionjoints such as Luer fittings. The inlet for receiving an aqueous liquidsample solution and outlet for liquid egress can be the same structureas where a beaker, flask or other vessel is used for a contemplatedseparation process, but the inlet and outlet are typically different andare separated from each other. Usually, the inlet and outlet are atopposite ends of the apparatus.

[0066]FIG. 1 provides a schematic drawing of one preferred separationapparatus. Here, the separation apparatus 10 is shown to include asupport vessel as a column 12 having an inlet 26 and an outlet 28 forliquid such as water. The outlet has an integral seal and is separablefrom the seal at a frangible connection 32. The separation apparatus 10contains one or more flow-permitting support elements. In oneembodiment, a frit 22 supports separation medium 16, and an upper frit18 helps to keep the separation medium in place during the introductionof an influent of aqueous sample or eluting solution. Contemplated fritscan be made of glass or plastic such as high-density polyethylene(HDPE). A HDPE frit of 35-45 μm average pore size is preferred. Acontemplated apparatus can also include a stopcock or otherflow-regulating device (not shown) at, near or in conjunction with theoutlet 28 to assist in regulating flow through the apparatus.

[0067] An above-described chromatographic column is typically offeredfor sale with a cap (not shown) placed into inlet 26 and snap-off(frangible) tube end 30. The separation medium in such a column istypically wet and equilibrated with about 0.05 to about 0.5 N HNO₃. Itis preferred that the average diameter of separation medium particles beabout 100 to about 150 μm when a chromatographic column separationapparatus is prepared and used.

[0068]FIG. 2 provides a second schematic drawing of another preferredseparation apparatus. Here, the separation apparatus 110 is shown toinclude a support vessel as a cartridge 112 having an inlet 126 and anoutlet 128 for liquid such as water. A cap 124 is preferably integrallymolded with the inlet 126. The outlet 128 is preferably integrallymolded with the cartridge 112. The separation apparatus 110 contains aporous support such as a frit 122 that supports separation medium 116.An upper porous support such as a frit 118 helps to keep the separationmedium in place during the introduction of an influent aqueous sample oreluting solution. A contemplated apparatus can also include a stopcockor other flow-regulating device (not shown) at, near or in conjunctionwith the outlet 128 to assist in regulating flow through the apparatus.

[0069] A contemplated cartridge such as a separation vessel of FIG. 2 istypically provided with the separation medium in a dry state, or atleast not wet with aqueous nitric acid. In addition, inlet 126 andoutlet 128 are preferably standard fittings such as Luer fittings thatare adapted for easy connection to other standard gas and/or liquidconnections. It is also preferred that the average diameter ofseparation particles be about 50 to about 100 μm when a cartridgeseparation apparatus is prepared and used.

[0070] One contemplated separation apparatus such as that of FIG. 1 canbe readily prepared by slurrying the separation medium in water oracidified water such as 0.5 normal nitric acid. The slurry is added ontoa flow-permitting support element such as a frit in a verticallyoriented support vessel such as a column. The separation medium ispermitted to settle under the force of gravity and can be packed moredensely using vibration, tapping or the like. Once a desired height ofseparation medium is achieved, any excess liquid is removed as byvacuum, a second flow-permitting element such as another frit isinserted into the column above the separation medium and the cap isadded.

[0071] To prepare another chromatographic column that can be used for acontemplated separation, a portion of separation medium prepared asdiscussed above is slurried in 0.5 M nitric acid and aliquots of thatslurry are transferred under nitrogen pressure to a 10 cm long glassBio-Rad® column (1.4 mm inside diameter) equipped with polypropylenefittings manufactured under the trademark “Cheminert” by Chromatronix,Inc., Berkeley, Calif. When the desired bed height is reached(corresponding to a bed volume of about 0.6 cm³), the separation mediumis resettled by backwashing. The separation medium is then rinsed withseveral bed volumes of 0.5 M nitric acid.

[0072] Chromatographic columns can similarly be prepared in othervessels such as 23 cm long glass Pasteur pipettes having a small glasswool plug (porous support) in the bottom and a layer of 80/100 meshglass beads on top of the separation medium to prevent disruption of thebed by sample introduction. Because these pipettes lack a liquid-holdingreservoir, sample solutions are introduced using a small polyethylenefunnel attached to the top of the pipette via a short length of vinyltubing. See, Dietz et al. (1996) J. Chem. Ed., 73(2):182-184.

[0073] A separation vessel shown in FIG. 2 can be prepared by adding apredetermined weight of dry separation medium to the cartridge 112containing molded outlet 128 and support frit 122. The thus filledcartridge is vibrated in a vertical orientation to achieve a constantheight for the separation medium bed, the upper porous support 118 isinserted, and the cap 124 containing molded fluid inlet 126 is placedonto the device.

[0074] Partition ratios for multivalent cations are measuredradiometrically using conventional procedures, and all measurements areperformed at 23 ±2° C. Gamma and beta counting are performed on aPackard® Cobra Gamma Counter and a Packard® Model 2200 LiquidScintillation Counter, respectively. Assessment of non-radioactiveelements is performed using well-known inductively-coupled plasma atomicemission spectroscopy.

[0075] The DF value for a given step is multiplied with the DF value forthe next step or, when represented using exponents, the DF valueexponents are added for each step. A DF value of about 10¹⁰ is about thelargest DF that can be readily determined using typical radioanalyticallaboratory apparatus.

[0076] The decontamination factor (DF) is defined using the followingequation:${DF} = \left( \frac{\frac{\lbrack{Analyte}\rbrack_{effluent}}{\lbrack{Impurity}\rbrack_{effluent}}}{\frac{\lbrack{Analyte}\rbrack_{influent}}{\lbrack{Impurity}\rbrack_{influent}}} \right)$

[0077] For a system at radioactive steady state (e.g., ²²⁹Th and itsdaughters including ²²⁵Ac, ²²⁵Ra and ²¹³Bi), the denominator is about 1.This means a DF value can be approximated by examining the strippingpeak in a chromatogram and dividing the maximum cpm/mL for the analyte(i.e., the desired ²²⁵Ac and ²²⁵Ra daughter radionuclides) by theactivity of the impurities (i.e., ²²⁹Th parent).

[0078] Alternatively, the DF value can be calculated by taking the ratioof the dry weight distribution ratios (D_(w)) for an analyte andimpurity. The dry weight distribution ratio is defined as:$D_{w} = {\left( \frac{A_{o} - A_{f}}{A_{f}} \right)\left( \frac{V}{m_{R} \cdot \left( {\% \quad {{solids}/100}} \right)} \right)}$

[0079] where A_(o)=the count rate in solution prior to contact with theresin, A_(f)=the count rate in solution after contact with resin,V=volume (mL) of solution in contact with resin, m_(R)=mass (g) of wetresin, and the % solids permits conversion to the dry mass of resin. Thesorption of various radioisotopes from nitric acid solution by aseparation medium is initially measured by contacting a known volume(typically 1.0 mL) of a spiked acid solution of appropriateconcentration with a known mass of medium. The ratio of the aqueousphase volume (mL) to the mass of the chromatographic materials (g)ranges from 70 to 180. (This ratio is determined primarily by the needto produce an easily measured decrease in the aqueous activity bycontact with the medium.) Although equilibrium is generally reached inless than 20 minutes, a 1 hour mixing time is normally employed.

[0080] The D_(w) values can be converted to the number of free columnvolumes to peak maximum (i.e., the resin capacity factor), k′, bydividing by approximately 2.19. This factor includes the conversion ofD_(w) to D (a volume partition ratio) and the value of the ratio of thevolume of stationary phase (v_(a)) to the volume of mobile phase (v_(m)), v_(a)/v_(m), typically observed for chromatographic columns packedwith the Strontium-selective resin (Eichrom Technologies, Inc.). (Theterm “stationary phase” refers to the volume of liquid extractingsolution contained in the pores of the support.)

[0081] Assuming that the “influent” is at radioactive steady state(making the denominator for DF unity), the ratio of D_(w) values foranalyte/impurity are:${DF} = \frac{\left( \frac{A_{o} - A_{f}}{A_{f}} \right)^{analyte}/\left( \frac{V}{m_{R} \cdot \left( {\% {\quad \quad}{{solids}/100}} \right)} \right)}{\left( \frac{A_{o} - A_{f}}{A_{f}} \right)^{impurity}/\left( \frac{V}{m_{R} \cdot \left( {\% \quad {{solids}/100}} \right)} \right)}$

[0082] which simplifies after cancellation to:${DF} = \frac{\left( \frac{A_{o} - A_{f}}{A_{f}} \right)^{analyte}}{\left( \frac{A_{o} - A_{f}}{A_{f}} \right)^{impurity}}$

[0083] where A_(o), A_(f), V, m_(R) and % solids are as previouslydefined. These ratios of activities are proportional to the molarconcentrations cited elsewhere in the definition of DF.

EXAMPLE 1 Synthesis of N,N,N′,N′-Tetra-n-octyl-diglycolamide (TO-DGA)

[0084] The synthesis of the TO-DGA is comparatively straightforwardusing commercially available reactants, requiring only 1-2 reactionsteps, and easy purification by an extractive process. The overallsynthesis and purification can be accomplished in less than sixperson-hours with about a 90% overall yield. An illustrative, not yetoptimized synthesis procedure for the production of 60 grams of theTO-DGA is detailed below.

[0085] All chemicals were purchased from Aldrich Chemical Co.,Milwaukee, Wis., and were used as received, except for the triethylaminethat was freshly distilled from calcium hydride before use. Allglassware was oven-dried prior to use and the reaction was carried outat ambient temperature. A positive pressure inert atmosphere of nitrogenwas maintained with a latex balloon and the reaction mixture was stirredmagnetically. Reactions on a larger scale require mechanical stirringbecause of the large amount of precipitate that formed.

[0086] A 500-mL single-neck round bottom flask was charged with drytetrahydrofuran (THF) (120 mL) and diglycolyl chloride (15.0 mL, 126mmol). The flask was partially immersed in a H₂O bath to dissipate heatfrom the mild exotherm. A dropping funnel was charged with dioctylamine(57.4 g, 238 mmol) and triethylamine (37.2 mL, 265 mmol) in THF (60 mL).

[0087] The amine solution was added drop-wise to the magneticallystirred reaction mixture over a period of about 1.5 hours. A whiteprecipitate of triethylammonium chloride immediately formed uponcombining the solutions. After addition of the amine solution wascomplete, the dropping funnel was rinsed with an additional 10 mL THF,which was added to the reaction mixture. The mixture was stirred for anadditional 1 hour, after which 10 mL H₂O was added. The THF wassubsequently removed by rotary evaporation.

[0088] To the pasty yellow residue was added 100 mL H₂O, creating aviscous orange upper phase and a colorless, cloudy lower phase. Thephases were separated in a separatory funnel and the lower phase wasextracted twice with 10 mL petroleum ether. The petroleum ether washeswere added to the initial upper phase that was extracted with 15 mL H₂O,2×15 mL 1 M HCl, 15 mL H₂O, and 20 mL 5% (w/v) NaHCO₃. Both resultingphases were cloudy orange.

[0089] After settling for about 18 hours, the two phases had not changedin appearance. The upper phase was extracted five times with 20 mL 5%NaHCO₃. The lower phases appeared to be emulsions after extraction andwere discarded. The upper phase was extracted with 10 mL 1 M HCl, 2×10mL H₂O, and 25 mL brine, dried over anhydrous MgSO₄, filteredgravitationally through fluted paper, and concentrated by rotaryevaporation. Yield: 62.92 g (91%) orange oil.

[0090] Similar preparations were carried out using other amines,including bis(2-ethylhexyl)-amine, and a repeat synthesis was carriedout using dioctylamine. The results of those syntheses and initialanalytical data are provided below in Table 1. TABLE 1 Analytical Datafor Diglycolamides of the Formula RR′NC (O) CH₂OCH₂ C (O) NRR′ Appear-Yield R R′ ance % NMR or MS Octyl Octyl Orange oil 94 ¹H NMR: 4.307 (s,4H); 3.291 (t, 4H, J=8 Hz); 3.177 (t, 4H, J=8 Hz); 1.519 (m, 8H); 1.272(br, 40H); 0.885 (t, 6H, J=6 Hz); 0.876 (t, 6H, J=6 Hz) LC-MS: 3.6 min(2%, m/z 358.2, calcd for dioctyl diamide C₂₀H₄₀N₂O₃.H⁺: 357.31); 4.06min (1%, m/z 469.3, calcd for trioctyl diamide C₂₈H₅₆N₂O₃.H⁺: 469.44);4.53 min (96%, m/z 581.4, calcd for tetraoctyl diamide C₃₆H₇₂N₂O₃.H⁺:581.56) 2-Ethyl- 2-Ethyl- Light 94 ¹H NMR: 4.330 (s, 4H); 3.37 hexylhexyl yellow oil (m, 4H); 3.043 (d, 4H, J=7 Hz); 1.669 (m, 3H); 1.560(m, 3H), 1.25 (m, 30H); 0.88 (m, 24H) LC-MS: 4.47 min (91%, m/z 581.4,calcd for tetra-(2- ethylhexyl)diamide C₃₆H₇₂N₂O₃.H⁺: 581.56), 5.50 min(9%, m/z 920.4). Hexyl Methyl Yellow oil 84 ¹H NMR: 4.314 (s, 4H); 4.293(s, 2H); 3.351 (t, 4H, J=8 Hz); 3.23 (t, 4H, J=8 Hz); 2.962 (s, 6H);2.920 (s, 6H); 1.529 (m, 8H); 0.885 (m, 12H) ESI-MS: 329.6 calcd forC₁₈H₃₆N₂O₃.H⁺: 329.28); 351.7 (calcd for C₁₈H₃₆N₂O₃.Na⁺: 351.26); 680.0(calcd for 2[C₁₈H₃₆N₂O₃].Na⁺: 679.97) Decyl Decyl Waxy 72 ¹H NMR: 4.300(s, 4H); 3.289 white (t, 4H, J=7.7 Hz); 3.171 solid (t, 4H, J=7.7 Hz);1.517 (m, 8H); 1.26 (br, 56H); 0.883 (t, 6H, J=7 Hz); 0.878 (t, 6H, J=7Hz) LC-MS: 3.3 min (2%, m/z every 44 amu from 532.2 to 796.2); 4.6 min(2%, m/z 581.4); 5.4 min (95%, m/z 693.5, calcd for tetradecyl diamideC₄₄H₈₈N₂O₃.H⁺: 693.69). Octyl H White 93 6.28 (br, 2H); 4.041 (s, 4H);flakes 3.311 (q, 4H, J=6.5 Hz); 1.54 (m, 4H); 1.3 (m. 20H), 0.883 (t,6H, J=7 Hz) LC-MS: 3.5 min (98%, m/z 357.2, calcd for dioctyl diamideC₂₀H₄₀N₂O₃.H⁺: 357.31), 5.3 min (2%, m/z 693.5).

[0091] NMR spectra were recorded in chloroform-d with tetramethylsilaneinternal reference using Varian Inova 400 MHz or 500 MHz spectrometers.MS was carried out using a PE Sciex API 150 EX Mass Spectrometer withESI probe, positive ion detection. LC-MS was carried out using aPhenomenex LUNA-C18-2 column, 100×4.6 mm, 20% water/80% acetonitrileeluent. Peak detection was by mass spectrometry using atmosphericpressure chemical ionization (APCI) and an ion trap mass spectrometer,positive ion detection.

EXAMPLE 2 Preparation of Yttrium (TO-DGA) Resin

[0092] The separation medium used herein containing TO-DGA was preparedusing a general procedure described previously for another separationmedium [Horwitz et al., Anal. Chem. 1991, 63, 522-525]. A portion ofTO-DGA (4.0 g) was dissolved in about 30 mL of CH₃OH and combined with50-100 μm Amberchrom®-CG71 particles (6.0 g) in about 20 mL of CH₃OH.The mixture was rotated at about 50° C. on a rotary evaporator for about30 minutes, after which the CH₃OH was vacuum distilled. After the bulkCH₃OH had been distilled, the free flowing resin was rotated under fullvacuum at about 40-50° C. for another 30 minutes to remove residualCH₃OH. The resulting solid is referred to as Yttrium Resin andcorresponds to 40% (w/w) loading of TO-DGA on 50-100 μm Amberchrom®-CG71particles.

EXAMPLE 3 Extraction Studies with Yttrium Resin

[0093] The TO-DGA molecules behave as neutral extractants; that is,solute loading occurs at high acid (e.g., nitric (HNO₃) or hydrochloric(HCl) acids) or salt concentrations (e.g., lithium nitrate (LiNO₃),lithium chloride (LiCl) or aluminum nitrate [Al(NO₃)₃] and stripping isaccomplished using dilute acid or salt solutions. One particularlynoteworthy characteristic of the TO-DGA resin, shown below, is the highuptake of polyvalent cations from 0.1-5 molar HNO₃ and the efficientstripping of these same cations using dilute (about 0.5 M or less) HCl.The elution behavior of several tri-, tetra-, and hexavalent cations onthe separation medium prepared (chromatographic material) usingN,N,N′,N′-tetra-n-octyl diglycolamide (TO-DGA) extractant describedbefore are shown below in Table 2. TABLE 2 Elution Behavior of SelectedCations on TO-DGA Resin* Percent of Total Fraction Bed Volume Al(III)Y(III) Th(IV) U(VI) Load(0.5 M HNO₃) 2.0 66 0 0 0 Rinse 2.0 28 0 0 75(0.1 M HNO₃) 2.0 0 0 0 8.4 2.0 0 0 0 0 2.0 0 0 0 0 2.0 0 0 0 0 Strip 2.00 24 78 0 (0.1 M HCl) 2.0 0 76 16 0 2.0 0 0 0 0 2.0 0 0 0 0 2.0 0 0 0 0

[0094] The negligible affinity of the TO-DGA resin for Al permitsconvenient purification of analytes from this frequently encounteredmatrix cation. The elution of U in 0.1 M HNO₃ while Th is retained isnoteworthy, as this separation can be accomplished at significantlylower acid concentrations than employed using conventional anionexchange resins or quaternary alkylamine extraction chromatographicmaterials. The extraction behavior of the TO-DGA resin is useful in theseparation and concentration of tri-, tetra-, and hexavalent cations andin the crossover from nitrate to chloride media (the medium of choicefor medical applications).

[0095] Data relevant to the use of the TO-DGA resin separation mediaincludes:

[0096] TO-DGA Formula Weight=580.98

[0097] Column Capacity:

[0098] 40% (w/w) TO-DGA on Amberchrom®-CG71

[0099] Bed density=0.35 g/mL of bed

[0100] 0.40×0.35=0.140 g of TO-DGA/mL of bed or

[0101] 0.241 mmol of TO-DGA/mL of bed

[0102] Column capacity for Sr²⁺ and Ra²⁺

[0103] Assume three TO-DGA per Sr²⁺ or Ra²⁺

[0104] 0.0803 mmol/mL of bed

[0105] Column capacity for Yb³⁺:

[0106] Assume 4 DGA per Yb³⁺:

[0107] 0.24/4=0.06 mmol of Yb³⁺/mL of bed

[0108] 11 mg of Yb³⁺/mL of bed

EXAMPLE 4 Uptake Results

[0109] Initial studies focused on the N,N,N′,N′-tetra-n-octyl derivativeof diglycolamide (DGA), and FIG. 3 shows the batch uptake results forBa(II), Ce(III), and Th(IV) as a function of nitric acid concentration([HNO₃]) on a separation medium containing 40% (w/w)N,N,N′,N′-tetra-n-octyl-DGA on Amberchrom®-CG71 particles as an inertresin support. The partitioning of Ce(III) and Th(Iv) increase steadilyup to about 3.0 M HNO₃, where the dry weight distribution ratio (D_(w))for Ce(III)=4.5×10³ and for Th(IV) D_(w)=1.0×10⁴.

[0110] Recovery of Ce(III) from the N,N,N′,N′-tetra-n-octyl-DGA resincan be readily accomplished using dilute HCl, as shown in FIG. 4. TheD_(w) values for Ce(III) decrease to less than 10 by 2.0 M HCl, whereasthe partitioning of Th(IV) plateaus in the D_(w)=10-20 range belowapproximately 0.50 M HCl. Barium(II) is not retained to any significantextent by N,N,N′,N′-tetra-n-octyl-DGA in either HNO₃ or HCl solutions,as shown in FIGS. 3 and 4.

EXAMPLE 5 Steric Effects on Diglycolamide Uptake

[0111] Additional studies targeting an understanding of the influence ofalkyl group size on trivalent cation selectivity exhibited by separationmedia containing 40% by weight of the N,N,N′,N′-tetra-n-octyl,N,N′-di-n-hexyl-N,N′-dimethyl, or N,N,N′,N′-tetra-(2-ethylhexyl)derivatives of DGA were undertaken.

[0112] The N,N′-di-n-hexyl-N,N′-dimethyl-DGA is expected to havediminished steric impact on the coordination and extraction mechanismsbecause of the shorter alkyl chains compared toN,N,N′,N′-tetra-n-octyl-DGA. Such short alkyl groups may result indiminished utility as an extraction chromatographic material, however,as the decreased lipophilicity of the extractant is anticipated to givea separation medium that is less stable with respect to extractantleaching during column chromatographic operations.

[0113] The N,N,N′,N′-tetra-(2-ethylhexyl)-substituted DGA permits a moredetailed investigation of steric crowding as the four 2-ethylhexylsubstituents are closer to the carbonyl oxygen donor sites that interactwith the cation during the extraction process. The effects of the2-ethylhexyl substituent on the selectivity of organophosphorus acidextractants is well-known, [Sekine et al. Solvent Extraction Chemistry:Fundamentals and Applications; Marcel Dekker: New York, 1977; andRydberg et al. Eds. Principles and Practices of Solvent Extraction;Marcel Dekker: New York, 1992] and N,N,N′,N′-tetra-(2-ethylhexyl)-DGArepresents an interesting neutral extractant for the study of trivalentlanthanide separations as N,N,N′,N′-tetran-octyl-DGA already hasdisplayed considerable selectivity for heavy lanthanide cations overlight lanthanide cations in various solvent extraction studies. [Sasakiet al. (2001) Solvent Extr. Ion Exch., 19:91-103; and Sasaki et al.(2002) Solvent Extr. Ion Exch., 20:21-34.]

[0114] The partitioning of Ce(III), Eu(III), and Y(III) (the latterrepresentative of a heavy lanthanide cation) byN,N,N′,N′-tetra-n-octyl-DGA resin as a function of [HNO₃] is shown inFIG. 5. The acid dependencies increase steadily from 0.010 M HNO₃ toapproximately 3.0 M HNO₃, where some leveling is observed for theheavier lanthanide cations. The intralanthanide separation factorsappear to maximize around 1.0 M HNO₃, with a separation factor forY(III) from Ce(III) (S^(y) _(ce)=(D_(w) for Y(III))/(D_(w) for Ce(III)))of 69 and S^(Y) _(Eu) of 5.8.

[0115] Because the partitioning of Eu(III) and Y(III) is considerable(i.e., D_(w) is about 10³ or more) at the comparatively lowconcentration of 0.10 M HNO₃, stripping of these solutes from theN,N,N′,N′-tetra-n-octyl-DGA resin is not practical using dilute HNO₃.FIG. 6 shows the dependence of D_(w) vs. [HCl], and it is evident thatCe(III) and Eu(III) can be readily stripped using less than 1.0 M HCl,whereas Y(III) plateaus in the D_(w)=30-80 range below 1.0 M HCl.Related chromatographic experiments have shown that Y(III) isefficiently eluted using 0.10 M HCl.

[0116]FIG. 7 shows the partitioning of Ce(III), Eu(III), and Y(III) byN,N′-di-n-hexyl-N,N′-dimethyl-DGA resin as a function of HNO₃concentration. The acid dependencies start at unusually high D_(w)values of greater than 10³ and increase with an approximate unit slope,which is unusual as the extraction of trivalent cations by neutralextractants typically afford slopes of approximately three to meetelectroneutrality requirements.

[0117] The absence of a clear dependence on [HNO₃] indicates thatstripping the loaded solutes from N,N′-di-n-hexyl-N,N′-dimethyl-DGAresin with HNO₃ is not practical in a commercial setting, and theprospects of stripping with HCl are equally poor in view of the data inFIG. 8. Shown here as a function of [HCl] are the D_(w) values forCe(III), Eu(III), and Y(III), which do not decrease appreciably (about200-3000) over the 0.010-8.0 M HCl range to afford any useful elutionconditions.

[0118] Further, any selectivity between the lanthanide analytes hasdisappeared and the comparatively flat acid dependencies raise questionsabout the mechanism of extraction. Such properties also point to aunique utility of this separation medium to extract these cations as asingle use separation medium that can extract selected cations and bediscarded or otherwise treated as a concentrated waste because thesolutes cannot be conveniently stripped by adjusting either the HNO₃ orHCl acid concentration. Thus, a mixture of trivalent and lower valentmaterials can be contacted with the separation medium resin and thetrivalent cations trapped on the resin.

[0119] The N,N,N′,N′-tetra-(2-ethylhexyl)-DGA molecule introduces alkylgroup branching and comparatively more steric hindrance near the site ofcation coordination. The data of FIG. 9 show the dependence of D_(w) forCe(III), Eu(III), and Y(III) vs. [HNO₃] forN,N,N′,N′-tetra-(2-ethylhexyl)-DGA resin, in which a greater aciddependence of D_(w) is observed than for the N,N,N′,N′-tetra-n-octylderivative (FIG. 5).

[0120] For example, N,N,N′,N′-tetra-n-octyl-DGA exhibits a D_(w)=5.0×10³at 0.10 M HNO₃ and D_(w)=2.4×10⁵ at 3.0 M HNO₃ for Y(III), whereasN,N,N′,N′-tetra(2-ethylhexyl)-DGA resin affords D_(w)=8.4 in 0.10 M HNO₃and D_(w)=9.3×10⁴ at 3.0 M HNO₃. Above 0.10 M HNO₃, the partitioning ofthese trivalent cations by N,N,N′,N′-tetra-(2-ethylhexyl)-DGA resinexhibits an acid dependence of approximately three, which is consistentwith the extraction of trivalent cations by neutral extractants. Thisbehavior contrasts with that observed in FIG. 5 forN,N,N′,N′-tetra-n-octyl-DGA resin, in which the slope over the 0.1-2 Mrange of HNO₃ is approximately two. Also noteworthy is the plateau inD_(w) exhibited by the N,N,N′,N′-tetra-n-octyl derivative aboveapproximately 2 M HNO₃, whereas partitioning byN,N,N′,N′-tetra-(2-ethylhexyl)-DGA increases steadily to the highestHNO₃ concentration of 8.0 M used in these studies.

[0121] The acid dependence for N,N,N′,N′-tetra-(2-ethylhexyl)-DGA shownin FIG. 9 illustrates the feasibility of stripping loaded solutes usingdilute HNO₃. This behavior is substantially different from thatexhibited by the N,N,N′,N′-tetra-n-octyl-DGA derivative (FIG. 5) inwhich retention of some cations in dilute HNO₃ is still significant.These results expand the utility of the DGA resins to those processesthan cannot tolerate HCl as a stripping agent.

[0122] The overall S^(Y) _(Ce) in 3.0 M HNO₃ is somewhat larger at 58for N,N,N′,N′-tetra-n-octyl-DGA resin than forN,N,N′,N′-tetra-(2-ethylhexyl)-DGA resin with S^(Y) _(Ce)=33.Interestingly, the S^(Y) _(Eu) values from 3.0 M HNO₃ are nearlyequivalent at 10 and 12 for the N,N,N′,N′-tetra-n-octyl-DGA andN,N,N′,N′-tetra-(2-ethylhexyl)-DGA resins, respectively.

[0123]FIG. 10 shows the HCl acid dependence for the same three cationsusing N,N,N′,N′-tetra-(2-ethylhexyl)-DGA resin, and these results aresimilar to those obtained for its straight chain n-octyl analog (FIG.6). The D_(w) values for these cations with theN,N,N′,N′-tetra-n-octyl-DGA and N,N,N′,N′-tetra(2-ethylhexyl)-DGA resinsdecrease to less than approximately 20 at 0.10 M HCl, which illustratesthe utility of these separation media for loading in concentrated HNO₃(or HCl) and stripping into dilute HCl solutions.

[0124] Although there are significant differences in the extractionproperties of separation media containing theN,N,N′,N′-tetra-n-octyl-DGA and N,N,N′,N′-tetra-(2-ethylhexyl)-DGAmolecules, such behavior cannot be unequivocally attributed to stericeffects based on the current data. In addition to steric considerations,different HNO₃ extraction behavior, self-aggregation characteristics,and any combination of these variables can contribute to the uniquebehavior exhibited by the n-octyl and 2-ethylhexyl derivatives of DGA.

EXAMPLE 6 Separation of Ac(III) and Ra(II)

[0125]FIG. 11 shows the results of a chromatographic study in which theability of the N,N,N′,N′-tetra-n-octyl-DGA resin to separate Ac(III)from Ra(II) present in 6.0 M HNO₃ is demonstrated. Over 90% of theRa(II) is eluted through the first bed volume of rinse, and moreextensive rinsing affords a better decontamination from Ra(II) in theAc(III) stripping regime. Some breakthrough of Ac(III) is observedduring the 9.5 bed volumes of load; however, these values are barelystatistically significant at just over twice background radiationlevels.

[0126] Stripping the N,N,N′,N′-tetra-n-octyl-DGA resin with 0.10 M HClremoves 96% of the Ac(III) in just five bed volumes. The stripping peakin FIG. 11 shows a maximum decontamination factor (DF) of Ac(III) fromRa(II) of more than 10², although more extensive rinsing is likely toincrease the DF to more than 10⁴.

EXAMPLE 7 Further Separation Studies

[0127] Table 3 summarizes the results of another chromatographic studyinvolving a separation medium comprised of N,N,N′,N′-tetra-n-octyl-DGAcoated on an inert resin (Amberchrom® CG-71, as discussed previously)and a variety of analytes. During the load phase, ≧90% of Ba(II),Cd(II), Cu(II), and Fe(III) elute in 4 M HNO₃, whereas Y(III) and Zr(IV)are strongly retained. Extensive rinsing with 0.5 M HNO₃ elutes theremaining quantities of Ba(II), Cd(II), Cu(II), and Fe(III), with norelease of Y(III) or Zr(IV). Only after four bed volumes of strip with0.01 M HCl is the Y(III) substantially eluted, whereas less than 50% ofthe Zr(IV) is eluted in a broad band covering 10 bed volumes. Theability of N,N,N′,N′-tetra-n-octyl-DGA separation medium to efficientlyseparate Y(III) from Fe(III) is notable, as the latter is ubiquitous inmany analytical and commercially important separations. TABLE 3 Elutionof selected cations on N,N,N′,N′-tetra-n-octyl-DGA resin. Bed Percent ofTotal Fraction Vols. Ba(II) Cd(II) Cu(II) Fe(III) Y(III) Zr(IV) Load 2090 93 95 92 0 0.9 (4 M HNO₃) Rinse 2.0 10 7 3.5 7 0 0.2 (0.5 M 2.0 <0.1<0.1 0.4 0.6 0 0 HNO₃) 2.0 <0.1 0 0.4 <.1 0 0 2.0 0 0 0.4 0.4 0 0 2.0 00 <0.1 0 0 0 Strip 2.0 0 0 0 0 71 5 (0.01 M 2.0 0 0 0 0 27 10 HCl) 2.0 00 0 0 1 11 2.0 0 0 0 0 0.7 10 2.0 0 0 0 0 0.3 10

[0128] Table 4, below, shows the elution behavior of several of thedivalent alkaline earth cations on N,N,N′,N′-tetra-n-octyl-DGA resin.During the 10 bed volumes of load with 4 M HNO₃, the majority of theMg(II) and Ba(II) elute, whereas Ca(II) and Sr(II) are retained. Theremaining Mg(II) and Ba(II) are essentially removed with the first bedvolume of rinse with 0.5 M HNO₃, and the Sr(II) is shown to elute underthese conditions. Interestingly, Ca(II) is retained by theN,N,N′,N′-tetra-n-octyl-DGA resin in 0.5 M HNO₃, but elutes in a ratherbroad band in 0.1 M HNO₃. The last vestiges of Ca(II) are removed ineight bed volumes of 0.1 M HCl. TABLE 4 Elution of selected cations onN,N,N′,N′-tetra-n-octyl-DGA resin Percent of Total Bed Fraction Vols.Mg(II) Ca(II) Sr(II) Ba(II) Load(4 M HNO₃) 10 94 1.1 0 96 Rinse 2 2.6<0.1 1.2 4 (0.5 M HNO₃) 2 0.5 0 96 0 2 0.2 0.1 2.4 0 2 0.8 0.2 0.4 0 20.5 0.2 <0.1 0 Rinse 2 0.1 28 <0.1 0 (0.1 M HNO₃) 2 0.1 63 0 0 2 0.1 3.40 0 2 0 1.1 0 0 2 0 1.1 0 0 Strip 4 0.1 1.1 0 0 (0.1 M HCl) 4 0.1 1.1 00

[0129] Related data for the N,N,N′,N′-tetra-n-octyl-DGA resin have shownthat Pb(II) behaves similarly to Sr(II) and that Ra(II) behavessimilarly to Ba(II). These data show that, under the appropriatesolution conditions, divalent cations can be retained by a separationmedium comprised of N,N,N′,N′-tetra-n-octyl-DGA resin and that someintra-alkaline earth separations can be effected using that separationmedium.

[0130] Each of the patents and articles cited herein is incorporated byreference. The use of the article “a” or “an” is intended to include oneor more.

[0131] The foregoing description and the examples are intended asillustrative and are not to be taken as limiting. Still other variationswithin the spirit and scope of this invention are possible and willreadily present themselves to those skilled in the art.

What is claimed:
 1. A separation medium comprising a diglycolamideextractant corresponding in structure to Formula I dispersed onto aninert support,

wherein R¹, R², R³ and R⁴ are the same or different and are hydrido orhydrocarbyl groups such that R¹+R²+R³+R⁴ contains about 14 to about 56carbon atoms.
 2. The separation medium according to claim 1 wherein saidinert support is porous.
 3. The separation medium according to claim 2wherein said porous, inert support is a resin.
 4. The separation mediumaccording to claim 3 wherein said resin is macroreticular.
 5. Theseparation medium according to claim 2 wherein said inert, poroussupport is silica.
 6. The separation medium according to claim 1 whereinsaid tetra-substituted diglycolamide extractant comprises about 3 toabout 50 weight percent of the total dry weight of the separationmedium.
 7. The separation medium according to claim 1 whereinR¹+R²+R³+R⁴ contains about 16 to about 40 carbon atoms.
 8. A separationmedium comprising a diglycolamide extractant corresponding in structureto Formula I dispersed onto a porous inert resin support, saiddiglycolamide comprising about 5 to about 50 weight percent of the totaldry weight of the separation medium,

wherein R¹, R², R³ and R⁴ are the same or different and are hydrido orhydrocarbyl groups such that R¹+R²+R³⁺R⁴ contains about 16 to about 40carbon atoms.
 9. The separation medium according to claim 8 wherein eachof R¹, R², R³ and R⁴ is a hydrocarbyl group.
 10. The separation mediumaccording to claim 8 wherein said diglycolamide extractant is presentdissolved in an organic diluent having a boiling point of about 170degrees to about 220 degrees C. at atmospheric pressure.
 11. Theseparation medium according to claim 10 wherein said diglycolamideextractant is present at about 0.1 to about 1.5 molar.
 12. Theseparation medium according to claim 8 wherein said separation medium ispresent as free flowing particles.
 13. The separation medium accordingto claim 8 wherein said diglycolamide extractant is present at about 10to about 40 weight percent of the total dry weight of the separationmedium.
 14. A separation medium comprising a diglycolamide extractantcorresponding in structure to Formula I dispersed onto a porous inertresin support, said diglycolamide comprising about 5 to about 50 weightpercent of the total dry weight of the separation medium, saidseparation medium being present as free flowing particles,

wherein R¹, R², R³ and R⁴ are the same or different hydrocarbyl groupssuch that R¹+R²+R³+R⁴ contains about 16 to about 40 carbon atoms. 15.The separation medium according to claim 14 wherein each of R¹, R², R³and R⁴ is an n-octyl group or a 2-ethylhexyl group.
 16. A method forseparating a preselected multivalent cation having a crystal ionicradius of about 0.8 to about 1.2 {dot over (A)}ngstroms (Å) from anaqueous sample comprising the steps of: (a) contacting a separationmedium of claim 1 with an aqueous sample containing an acid or saltingout amount of one or more acids or salting out agents for a neutralextractant and dissolved multivalent cations, including saidpredetermined multivalent cation; (b) maintaining said contact for atime period sufficient for the predetermined multivalent cations to beextracted from the sample solution to the separation medium to form asolid phase loaded separation medium and a liquid phase multivalentcation-depleted sample; and (c) separating said solid and liquid phases.17. The method according to claim 16 wherein said multivalent cationsare pseudo-lanthanide, prelanthanide, lanthanide, preactinide oractinide cations.
 18. The method according to claim 17 wherein saidpreactinide or pseudo-lanthanide multivalent cation is an actinium oryttrium cation.
 19. The method according to claim 16 wherein saidmultivalent cations are eluted by contacting said loaded separationmedium with water or dilute hydrochloric or nitric acid.
 20. The methodaccording to claim 16 wherein said contacting of step (a) is carried outin a chromatographic separation column by passing said aqueous acidicsample solution through a chromatographic separation column containingsaid separation medium.
 21. The method according to claim 16 whereinactinium or yttrium cations are loaded on said separation medium and areeluted from said loaded separation medium by passing dilute hydrochloricacid through the loaded separation medium in a separation column. 22.The method according to claim 16 wherein said separation mediumcomprises a diglycolamide extractant corresponding in structure toFormula I dispersed onto a porous inert resin support, saiddiglycolamide comprising about 10 to about 40 weight percent of thetotal dry weight of the separation medium,

wherein R¹, R², R³ and R⁴ are the same or different and are hydrido orhydrocarbyl groups such that R¹+R²+R³+R⁴ contains about 16 to about 40carbon atoms.
 23. The method according to claim 16 wherein said inert,porous support is silica.
 24. The method according to claim 16 whereineach of R¹, R², R³ and R⁴ is a hydrocarbyl group.
 25. A method forseparating actinium or yttrium cations from an aqueous sample comprisingthe steps of: (a) passing an acidic aqueous sample containing dissolvedactinium or yttrium cations into a separation apparatus comprising aseparation vessel that contains separation medium to contact saidseparation medium with said aqueous acidic sample solution, saidseparation medium comprising N,N,N′,N′-tetra-n-octyl diglycolamide orN,N,N′,N′-tetra-(2-ethylhexyl) diglycolamide dispersed onto an inert,porous, particulate resin support, said separation medium beingfree-flowing when dry; (b) maintaining said contact for a time periodsufficient for the actinium or yttrium cations to be extracted from thesample solution to the separation medium to form a solid phase loadedseparation medium and a liquid phase alkaline earth cation-depletedsample; (c) separating said solid and liquid phases; and (d) elutingsaid actinium or yttrium cations from said loaded separation medium bypassing an aqueous dilute hydrochloric acid solution through the loadedseparation medium in said separation apparatus.
 26. The method accordingto claim 25 wherein said N,N,N′,N′-tetra-n-octyl diglycolamide or theN,N,N′,N′-tetra-(2-ethylhexyl) diglycolamide comprises about 10 to about40 weight percent of the total dry weight of the separation medium. 27.An apparatus for separating pseudo-lanthanide, prelanthanide,lanthanide, preactinide or actinide cations from an acidic aqueoussample that comprises: a vessel having an inlet, an outlet andseparation medium in a separation medium-containing region wherein theseparation medium is supported and contained within the separationmedium-containing region; said separation medium comprising adiglycolamide extractant corresponding in structure to Formula Idispersed onto an inert, porous support,

wherein R¹, R², R³ and R⁴ are the same or different and are hydrido orhydrocarbyl groups such that R¹+R²+R³+R⁴ contains about 14 to about 56carbon atoms.
 28. The separation apparatus according to claim 27 whereinsaid vessel includes a first flow-permitting support positioned betweenthe outlet and the medium-containing region.
 29. The separationapparatus according to claim 28 wherein said vessel includes a secondflow-permitting support positioned between the inlet and themedium-containing region.
 30. The separation apparatus according toclaim 27 wherein said inlet and outlet are separated from each other.31. The separation apparatus according to claim 30 wherein said inletand outlet are at opposite ends of the apparatus.
 32. The separationapparatus according to claim 27 wherein said separation medium comprisesN,N,N′,N′-tetra-n-octyl diglycolamide or N,N,N′,N′-tetra-(2-ethylhexyl)diglycolamide dispersed onto an inert macroreticular resin support. 33.The separation apparatus according to claim 32 wherein saidN,N,N′,N′-tetraoctyl diglycolamide or N,N,N′,N′-tetra-(2-ethylhexyl)diglycolamide comprises-about 5 to about 50 weight percent of the totaldry weight of the separation medium.
 34. The separation apparatusaccording to claim 27 wherein said diglycolamide extractant is dissolvedin an organic diluent having a boiling point of about 170 degrees toabout 220 degrees C at atmospheric pressure. 35.N,N,N′,N′-tetra-(2-ethylhexyl) diglycolamide.